Glass fibers used as reinforcing elements in polymeric or resinous matrix materials are usually coated with a very light-weight size coating which serves to protect the fibers from damage by abrasion during processing, handling and/or use, to bind the individual fibers into more-or-less tightly integrated multi-fiber bundles or strands, and/or to enhance the reinforcing interaction between the fibers and the resinous matrix in which they are imbedded as reinforcing elements. Such sizing compositions are frequently applied to the glass fibers at the time of their initial production, which is ordinarily by pulling a plurality of streams of molten glass issuing from a reservoir thereof through a substantially corresponding plurality of suitable orifices so as to attenuate these streams to the desired fiber diameter as they cool and solidify. The sizing composition is typically applied to the individual fibers in-line as soon as they have cooled sufficiently below the solidification temperature, which cooling may be accelerated by wetting the newly solidified but still hot fibers with water. Liquid sizing compositions are applied in such situations by spraying, by drawing the fibers across a suitable roll, belt, apron, pad, etc. wet with the liquid sizing composition, or other conventional liquid coating methods. After the liquid sizing composition has been applied to the individual advancing glass fibers, they are typically brought together while still at least partially wet with the liquid sizing composition into one or more multifiber bundles or strands, which may be collected into a suitable package for further processing, storage and/or shipment, as by winding onto a rotating collet. The wet fibers or strands are normally dried, before and/or after such collection, to deposit the non-volatile residue of the liquid sizing composition onto the surfaces of the fibers.
Liquid sizing compositions suitable for such application to glass fibers ordinarily are dilute solutions, dispersions and/or emulsions, often in aqueous media, of a film-forming polymer or resin, a lubricant and a coupling agent. Other components, such as anti-static agents (especially where the sized glass fibers are to be chopped into short lengths while dry), emulsifying or solubilizing agents, viscosity modifying agents, etc. have also sometimes been incorporated in such liquid sizing compositions.
One of the uses for glass fibers is as gun roving, which desirably consists of a plurality of continuous strands weakly integrated together, with each strand consisting of a plurality of individual glass fibers tightly integrated together by the size coating on the fibers. Such gun roving is used by feeding it through a suitable chopper incorporated in or closely associated with a suitable gun for spraying a fluid resin composition together with the chopped roving onto a mold or other suitable target so that the chopped roving or pieces of strand separated therefrom becomes imbedded in the fluid resin, which will subsequently be solidified by cooling and/or by curing by chemical reaction. Representative equipment and corresponding methods for such use of glass fibers in gun roving are described in U.S. Pat. No. 3,111,440, entitled DEVICES AND METHODS FOR APPLYING STRANDS, issued Nov. 19, 1963 for an invention of William H. Prentice, incorporated herein by reference. Typically, the chopped pieces are from about 1/2 to about 2 inches in length.
Glass fiber gun roving has heretofore been coated with liquid sizing compositions containing Werner-type chrome complexes, such as methacrylato chromic chloride, which is thought to function in part at least as a glass-resin coupling agent, although such chrome complexes have sometimes been used together with conventional organosilane glass-resin coupling agents. Before the present invention it had not been thought possible to achieve a satisfactory balance of desirable properties in glass fiber gun roving without the inclusion of a chrome complex in the sizing composition for the constituent fibers thereof, and particularly to achieve a desirable ease and completeness of chopping in conventional equipment, while also achieving desirably rapid and complete wetting of the chopped reinforcement by the liquid matrix resin composition and providing a desirable enhancement of the physical properties of the resinous matrix while holding the generation of fuzz, from breakage of fibers during processing of the continuous strand or roving, and "fly", i.e., static-dispersed pieces of chopped roving strand or partially or fully fibrillated residues thereof accompanying the chopping and spraying at the gun, to desirably low incidence.